Liquefied Natural Gas Production

ABSTRACT

Hydrocarbon processing systems and a method for liquefied natural gas (LNG) production are described herein. The hydrocarbon processing system includes a fluorocarbon refrigeration system configured to cool a natural gas to produce LNG using a mixed fluorocarbon refrigerant and a nitrogen rejection unit (NRU) configured to remove nitrogen from the LNG.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication 61/756,322 filed 24 Jan. 2013 entitled LIQUEFIED NATURAL GASPRODUCTION, the entirety of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present techniques relate generally to the field of hydrocarbonrecovery and treatment processes and, more particularly, to a method andsystems for liquefied natural gas (LNG) production via a refrigerationprocess that uses mixed fluorocarbon refrigerants.

BACKGROUND

This section is intended to introduce various aspects of the art, whichmay be associated with exemplary embodiments of the present techniques.This discussion is believed to assist in providing a framework tofacilitate a better understanding of particular aspects of the presenttechniques. Accordingly, it should be understood that this sectionshould be read in this light, and not necessarily as admissions of priorart.

Many low temperature refrigeration systems that are used for natural gasprocessing and liquefaction rely on the use of single componentrefrigerants or mixed refrigerants (MRs) including hydrocarbonscomponents to provide external refrigeration. For example, liquefiednatural gas (LNG) may be produced using a mixed refrigerant includinghydrocarbon components extracted from a feed gas. Such hydrocarboncomponents may include methane, ethane, ethylene, propane, and the like.

U.S. Pat. No. 6,412,302 to Foglietta et al. describes a process forproducing a liquefied natural gas stream. The process includes coolingat least a portion of a pressurized natural gas feed stream by heatexchange contact with first and second expanded refrigerants that areused in independent refrigeration cycles. The first expanded refrigerantis selected from methane, ethane, and treated and pressurized naturalgas, while the second expanded refrigerant is nitrogen. Therefore, suchtechniques rely on the use of refrigerants including hydrocarbons, whichare flammable.

U.S. Patent Application Publication No. 2010/0281915 by Roberts et al.describes a system and method for liquefying a natural gas stream. Adehydrated natural gas stream is pre-cooled in a pre-cooling apparatusthat uses a pre-coolant consisting of a HFC refrigerant. The pre-cooleddehydrated natural gas stream is then cooled in a main heat exchangerthrough indirect heat exchange against a vaporized hydrocarbon mixedrefrigerant coolant to produce LNG. The mixed refrigerant coolantincludes ethane, methane, nitrogen, and less than or equal to 3 mol % ofpropane. Therefore, such techniques also rely on the use of refrigerantsincluding hydrocarbons.

U.S. Patent Application Publication No. 2012/0047943 by Barclay et al.describes a process for offshore liquefaction of a natural gas feed. Theprocess includes contacting the natural gas feed with a biphasicrefrigerant at a first temperature, contacting the natural gas feed witha first gaseous refrigerant at a second temperature, and contacting thenatural gas feed with a second gaseous refrigerant at a thirdtemperature. The refrigerated natural gas feed is then expanded using anexpansion device to form a flash gas stream and a liquefied natural gasstream. The biphasic refrigerant may be a commercial refrigerant such asR507 or R134a, or a mixture thereof. The first gaseous refrigerant maybe nitrogen. The second gaseous refrigerant may be the flash gas streamrecovered from the natural gas feed. The biphasic refrigerant is used tocool and partially condense the natural gas feed in a feed gas chiller,while the first and second gaseous refrigerants are used to cool andcondense the natural gas feed in a main cryogenic heat exchanger.Therefore, such techniques rely on the use of a refrigerant includinghydrocarbon components extracted from the natural gas feed.

U.S. Pat. No. 6,631,625 to Weng describes a non-hydrochlorofluorocarbon(non-HCFC) design of a refrigerant mixture for an ultra-low temperaturerefrigeration system. The non-HCFC refrigerant mixture is primarilycomposed of hydrofluorocarbon (HFC) refrigerants and hydrocarbons.Therefore, such techniques also rely on the use of refrigerantsincluding hydrocarbons. Furthermore, the use of such refrigerantmixtures for natural gas processing or liquefaction is not disclosed.

SUMMARY

An embodiment provides a hydrocarbon processing system for liquefiednatural gas (LNG) production. The hydrocarbon processing system includesa fluorocarbon refrigeration system configured to cool a natural gas toproduce LNG using a mixed fluorocarbon refrigerant and a nitrogenrejection unit (NRU) configured to remove nitrogen from the LNG.

Another embodiment provides a method for liquefied natural gas (LNG)production. The method includes cooling a natural gas to produce LNG ina fluorocarbon refrigeration system using a mixed fluorocarbonrefrigerant and removing nitrogen from the LNG in a nitrogen rejectionunit (NRU).

Another embodiment provides a hydrocarbon processing system for theformation of a liquefied natural gas (LNG). The hydrocarbon processingsystem includes a mixed refrigerant cycle configured to cool a naturalgas using a mixed fluorocarbon refrigerant, wherein the mixedrefrigerant cycle includes a heat exchanger configured to allow forcooling of the natural gas via an indirect exchange of heat between thenatural gas and the mixed fluorocarbon refrigerant. The hydrocarbonprocessing system also includes a nitrogen rejection unit (NRU)configured to remove nitrogen from the natural gas and a methaneautorefrigeration system configured to cool the natural gas to producethe LNG.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the present techniques are better understood byreferring to the following detailed description and the attacheddrawings, in which:

FIG. 1 is a process flow diagram of a single stage refrigeration system;

FIG. 2 is a process flow diagram of a two stage refrigeration systemincluding an economizer;

FIG. 3 is a process flow diagram of a single stage refrigeration systemincluding a heat exchanger economizer;

FIG. 4 is a process flow diagram of a liquefied natural gas (LNG)production system;

FIG. 5 is a process flow diagram of a hydrocarbon processing systemincluding a single mixed refrigerant (SMR) cycle;

FIG. 6 is a process flow diagram of the hydrocarbon processing system ofFIG. 5 with the addition of a nitrogen refrigeration system;

FIG. 7 is a process flow diagram of the hydrocarbon processing system ofFIG. 5 with the addition of a methane autorefrigeration system;

FIG. 8 is a process flow diagram of a hydrocarbon processing systemincluding a pre-cooled SMR cycle;

FIG. 9 is a process flow diagram of a hydrocarbon processing systemincluding a dual mixed refrigerant (DMR) cycle;

FIGS. 10A and 10B are process flow diagrams of a hydrocarbon processingsystem including an SMR cycle, an NRU, and a methane autorefrigerationsystem;

FIGS. 11A and 11B are process flow diagrams of a hydrocarbon processingsystem including an economized DMR cycle, an NRU, and a methaneautorefrigeration system; and

FIG. 12 is a process flow diagram of a method for the formation of LNGfrom a natural gas stream using a mixed fluorocarbon refrigerant.

DETAILED DESCRIPTION

In the following detailed description section, specific embodiments ofthe present techniques are described. However, to the extent that thefollowing description is specific to a particular embodiment or aparticular use of the present techniques, this is intended to be forexemplary purposes only and simply provides a description of theexemplary embodiments. Accordingly, the techniques are not limited tothe specific embodiments described herein, but rather, include allalternatives, modifications, and equivalents falling within the spiritand scope of the appended claims.

At the outset, for ease of reference, certain terms used in thisapplication and their meanings as used in this context are set forth. Tothe extent a term used herein is not defined herein, it should be giventhe broadest definition persons in the pertinent art have given thatterm as reflected in at least one printed publication or issued patent.Further, the present techniques are not limited by the usage of theterms shown herein, as all equivalents, synonyms, new developments, andterms or techniques that serve the same or a similar purpose areconsidered to be within the scope of the present claims.

As used herein, “autorefrigeration” refers to a process whereby aportion of a product stream is used for refrigeration purposes. This isachieved by extracting a fraction of the product stream prior to finalcooling for the purpose of providing refrigeration capacity. Thisextracted stream is expanded in a valve or expander and, as a result ofthe expansion, the temperature of the stream is lowered. This stream isused for cooling the product stream in a heat exchanger. Afterexchanging heat, this stream is recompressed and blended with the feedgas stream. This process is also known as open cycle refrigeration.

Alternatively, “autorefrigeration” refers to a process whereby a fluidis cooled via a reduction in pressure. In the case of liquids,autorefrigeration refers to the cooling of the liquid by evaporation,which corresponds to a reduction in pressure. More specifically, aportion of the liquid is flashed into vapor as it undergoes a reductionin pressure while passing through a throttling device. As a result, boththe vapor and the residual liquid are cooled to the saturationtemperature of the liquid at the reduced pressure. For example,according to embodiments described herein, autorefrigeration of anatural gas may be performed by maintaining the natural gas at itsboiling point so that the natural gas is cooled as heat is lost duringboil off. This process may also be referred to as “flash evaporation.”

The “boiling point” or “BP” of a substance is the temperature at whichthe vapor pressure of the liquid equals the pressure surrounding theliquid and, thus, the liquid changes into a vapor. The “normal boilingpoint” or “NBP” of a substance is the boiling point at a pressure of oneatmosphere, i.e., 101.3 kilopascals (kPa).

A “compressor” includes any unit, device, or apparatus able to increasethe pressure of a stream. This includes compressors having a singlecompression process or step, or compressors having multi-stagecompression processes or steps, more particularly multi-stagecompressors within a single casing or shell. Evaporated streams to becompressed can be provided to a compressor at different pressures. Forexample, some stages or steps of a hydrocarbon cooling process mayinvolve two or more refrigerant compressors in parallel, series, orboth. The present techniques are not limited by the type or arrangementor layout of the compressor or compressors, particularly in anyrefrigeration cycle.

As used herein, “cooling” broadly refers to lowering and/or dropping atemperature and/or internal energy of a substance, such as by anysuitable amount. Cooling may include a temperature drop of at leastabout 1° C., at least about 5° C., at least about 10° C., at least about15° C., at least about 25° C., at least about 50° C., at least about100° C., and/or the like. The cooling may use any suitable heat sink,such as steam generation, hot water heating, cooling water, air,refrigerant, other process streams (integration), and combinationsthereof. One or more sources of cooling may be combined and/or cascadedto reach a desired outlet temperature. The cooling step may use acooling unit with any suitable device and/or equipment. According to oneembodiment, cooling may include indirect heat exchange, such as with oneor more heat exchangers. Heat exchangers may include any suitabledesign, such as shell and tube, brazed aluminum, spiral wound, and/orthe like. In the alternative, the cooling may use evaporative (heat ofvaporization) cooling, sensible heat cooling, and/or direct heatexchange, such as a liquid sprayed directly into a process stream.

“Cryogenic temperature” refers to a temperature that is about −50° C. orbelow.

As used herein, the terms “deethanizer” and “demethanizer” refer todistillation columns or towers that may be used to separate componentswithin a natural gas stream. For example, a demethanizer is used toseparate methane and other volatile components from ethane and heaviercomponents. The methane fraction is typically recovered as purified gasthat contains small amounts of inert gases such as nitrogen, CO₂, or thelike.

“Fluorocarbons,” also referred to as “perfluorocarbons” or “PFCs,” aremolecules including F and C atoms. Fluorocarbons have F—C bonds and,depending on the number of carbon atoms in the species, C—C bonds. Anexample of a fluorocarbon includes hexafluoroethane (C₂F₆).“Hydrofluorocarbons” or “HFCs” are a specific type of fluorocarbonincluding H, F, and C atoms. Hydrofluorocarbons have H—C and F—C bondsand, depending on the number of carbon atoms in the species, C—C bonds.Some examples of hydrofluorocarbons include fluoroform (CHF₃),pentafluoroethane (C₂HF₅), tetrafluoroethane (C₂H₂F₄),heptafluoropropane (C₃HF₇), hexafluoropropane (C₃H₂F₆),pentafluoropropane (C₃H₃F₅), and tetrafluoropropane (C₃H₄F₄), amongother compounds of similar chemical structure. Hydrofluorocarbons withunsaturated bonds are referred to as “hydrofluoroolefins” or “HFOs.”HFOs are typically more reactive and flammable than HFCs due to thepresence of unsaturated bonds. However, HFOs also typically degrade inthe environment faster than HFCs.

The term “gas” is used interchangeably with “vapor,” and is defined as asubstance or mixture of substances in the gaseous state as distinguishedfrom the liquid or solid state. Likewise, the term “liquid” means asubstance or mixture of substances in the liquid state as distinguishedfrom the gas or solid state.

The term “greenhouse gases” broadly refers to gases or vapors in anatmosphere that can absorb and/or emit radiation within the thermalinfrared range. Examples include carbon monoxide, carbon dioxide, watervapor, methane, ethane, propane, ozone, hydrogen sulfide, sulfur oxides,nitrogen oxides, halocarbons, chlorofluorocarbons, or the like.Electrical power plants, petroleum refineries, and other energyconversion facilities can tend to be large sources of greenhouses gasesemitted to the atmosphere. Without being bound by theory, greenhousegases are believed to receive and/or retain solar radiation and energy,which become trapped in the atmosphere. This may result in an increasein average global atmospheric temperatures and other climate changes.

The “global-warming potential” or “GWP” of a gas is a relative measureof how much heat the gas traps in the atmosphere. GWP compares theamount of heat trapped by a certain mass of the gas in question to theamount of heat trapped by a similar mass of carbon dioxide. GWP iscalculated over a specific time interval, such as 20, 100 or 500 years.GWP is expressed as a factor of carbon dioxide, wherein carbon dioxidehas a standardized GWP of 1. For example, the 20 year GWP, i.e., GWP₂₀,of methane is 72. This means that, if the same mass of methane andcarbon dioxide are introduced into the atmosphere, the methane will trap72 times more heat than the carbon dioxide over the next 20 years.

A “heat exchanger” broadly means any device capable of transferring heatfrom one media to another media, including particularly any structure,e.g., device commonly referred to as a heat exchanger. Heat exchangersinclude “direct heat exchangers” and “indirect heat exchangers.” Thus, aheat exchanger may be a shell-and-tube, spiral, hairpin, core,core-and-kettle, double-pipe, brazed aluminum, spiral wound, or anyother type of known heat exchanger. “Heat exchanger” may also refer toany column, tower, unit or other arrangement adapted to allow thepassage of one or more streams there through, and to affect direct orindirect heat exchange between one or more lines of refrigerant, and oneor more feed streams.

A “hydrocarbon” is an organic compound that primarily includes theelements hydrogen and carbon, although nitrogen, sulfur, oxygen, metals,or any number of other elements may be present in small amounts. As usedherein, hydrocarbons generally refer to components found in natural gas,oil, or chemical processing facilities.

“Liquefied natural gas” or “LNG” is natural gas generally known toinclude a high percentage of methane. However, LNG may also includetrace amounts of other compounds. The other elements or compounds mayinclude, but are not limited to, ethane, propane, butane, carbondioxide, nitrogen, helium, hydrogen sulfide, or combinations thereof,that have been processed to remove one or more components (for instance,helium) or impurities (for instance, water and/or heavy hydrocarbons)and then condensed into a liquid at almost atmospheric pressure bycooling.

“Liquefied petroleum gas” or “LPG” generally refers to a mixture ofpropane, butane, and other light hydrocarbons derived from refiningcrude oil. At normal temperature, LPG is a gas. However, LPG can becooled or subjected to pressure to facilitate storage andtransportation.

The “melting point” or “MP” of a substance is the temperature at whichthe solid and liquid forms of the substance can exist in equilibrium. Asheat is applied to the solid form of a substance, its temperature willincrease until the melting point is reached. The application ofadditional heat will then convert the substance from solid form toliquid form with no temperature change. When the entire substance hasmelted, additional heat will raise the temperature of the liquid form ofthe substance.

“Mixed refrigerant processes” or “MR processes” may include, but are notlimited to, a “single mixed refrigerant” or “SMR” cycle, a hydrocarbonpre-cooled MR cycle, a “dual mixed refrigerant” or “DMR” cycle, and a“triple mixed refrigerant” or “TMR” cycle. In general, MRs can includehydrocarbon and/or non-hydrocarbon components. MR processes employ atleast one mixed component refrigerant, but can additionally employ oneor more pure-component refrigerants as well.

“Natural gas” refers to a multi-component gas obtained from a crude oilwell or from a subterranean gas-bearing formation. The composition andpressure of natural gas can vary significantly. A typical natural gasstream contains methane (CH₄) as a major component, i.e., greater than50 mol % of the natural gas stream is methane. The natural gas streamcan also contain ethane (C₂H₆), higher molecular weight hydrocarbons(e.g., C₃-C₂₀ hydrocarbons), one or more acid gases (e.g., carbondioxide or hydrogen sulfide), or any combinations thereof. The naturalgas can also contain minor amounts of contaminants such as water,nitrogen, iron sulfide, wax, crude oil, or any combinations thereof. Thenatural gas stream may be substantially purified prior to use inembodiments, so as to remove compounds that may act as poisons.

As used herein, “natural gas liquids” or “NGLs” refer to mixtures ofhydrocarbons whose components are, for example, typically heavier thanmethane and condensed from a natural gas. Some examples of hydrocarboncomponents of NGL streams include ethane, propane, butane, and pentaneisomers, benzene, toluene, and other aromatic compounds.

A “nitrogen rejection unit” or “NRU” refers to any system or deviceconfigured to receive a natural gas feed stream and producesubstantially pure products streams, e.g., a salable methane stream anda nitrogen stream including about 30% to 99% N₂. Examples of types ofNRU's include cryogenic distillation, pressure swing adsorption (PSA),membrane separation, lean oil absorption, and solvent absorption.

The “ozone depletion potential” or “ODP” of a chemical compound is therelative amount of degradation to the ozone layer it can cause, wheretrichlorofluoromethane, i.e., R-11, is fixed at an ODP of 1.0.Chlorodifluoromethane, i.e., R-22, for example, has an ODP of 0.055.Many HFCs, such as R-32, have ODPs approaching zero.

A “refrigerant component,” in a refrigeration system, will absorb heatat a lower temperature and pressure through evaporation and will rejectheat at a higher temperature and pressure through condensation.Illustrative refrigerant components may include, but are not limited to,alkanes, alkenes, and alkynes having one to five carbon atoms, nitrogen,chlorinated hydrocarbons, fluorinated hydrocarbons, other halogenatedhydrocarbons, noble gases, and mixtures or combinations thereof.

Refrigerant components often include single component refrigerants. Asingle component refrigerant with a single halogenated hydrocarbon hasan associated “R-” designation of two or three numbers, which reflectsits chemical composition. Adding 90 to the number gives three digitsthat stand for the number of carbon, hydrogen, and fluorine atoms,respectively. The first digit of a refrigerant with three numbers is oneunit lower than the number of carbon atoms in the molecule. If themolecule contains only one carbon atom, the first digit is omitted. Thesecond digit is one unit greater than the number of hydrogen atoms inthe molecule. The third digit is equal to the number of fluorine atomsin the molecule. Remaining bonds not accounted for are occupied bychlorine atoms. A suffix of a lower-case letter “a,” “b,” or “c”indicates increasingly unsymmetrical isomers. As a special case, theR-400 series is made up of zeotropic blends, and the R-500 series ismade up of azeotropic blends. The rightmost digit is assignedarbitrarily by ASHRAE, an industry organization.

“Substantial” when used in reference to a quantity or amount of amaterial, or a specific characteristic thereof, refers to an amount thatis sufficient to provide an effect that the material or characteristicwas intended to provide. The exact degree of deviation allowable maydepend, in some cases, on the specific context.

Overview

Embodiments described herein provide a hydrocarbon processing system.The hydrocarbon processing system includes a refrigeration system forproducing LNG from a natural gas. The refrigeration system includes afluorocarbon refrigeration system that utilizes a mixed fluorocarbonrefrigerant to cool the natural gas. The refrigeration system may alsoinclude a nitrogen refrigeration system and/or a methaneautorefrigeration system, which may be used to further cool the naturalgas to produce LNG. In addition, the hydrocarbon processing system mayinclude an NRU, which may be used to remove nitrogen from the naturalgas. In some embodiments, the nitrogen that is removed from the naturalgas via the NRU is used to provide additional cooling for the naturalgas.

Hydrocarbon processing systems include any number of systems known tothose skilled in the art. Hydrocarbon production and treatment processesinclude, but are not limited to, chilling natural gas for NGLextraction, chilling natural gas for hydrocarbon dew point control,chilling natural gas for CO₂ removal, LPG production storage,condensation of reflux in deethanizers or demethanizers, and natural gasliquefaction to produce LNG.

Although many refrigeration cycles have been used to processhydrocarbons, one cycle that is used in LNG liquefaction plants is thecascade cycle, which uses multiple single component refrigerants in heatexchangers arranged progressively to reduce the temperature of the gasto a liquefaction temperature. Another cycle that is used in LNGliquefactions plants is the multi-component refrigeration cycle, whichuses a multi-component refrigerant in specially designed exchangers. Inaddition, another cycle that is used in LNG liquefaction plants is theexpander cycle, which expands gas from feed gas pressure to a lowpressure with a corresponding reduction in temperature. Natural gasliquefaction cycles may also use variations or combinations of thesethree cycles.

LNG is prepared from a feed gas by refrigeration and liquefactiontechnologies. Optional steps include condensate removal, CO₂ removal,dehydration, mercury removal, nitrogen stripping, H₂S removal, and thelike. After liquefaction, LNG may be stored or loaded on a tanker forsale or transport. Conventional liquefaction processes can include: APCIPropane pre-cooled mixed refrigerant; C₃MR; DUAL MR; Phillips OptimizedCascade; Prico SMR; TEAL dual pressure mixed refrigerant; Linde/Statoilmulti fluid cascade; Axens DMR; ExxonMobil's Enhanced Mixed Refrigerant(EMR); and the Shell processes C₃MR and DMR.

Carbon dioxide removal, i.e., separation of methane and lighter gasesfrom CO₂ and heavier gases, may be achieved with cryogenic distillationprocesses, such as the Controlled Freeze Zone technology available fromExxonMobil Corporation.

While the method and systems described herein are discussed with respectto the formation of LNG from natural gas, the method and systems mayalso be used for a variety of other purposes. For example, the methodand systems described herein may be used to chill natural gas forhydrocarbon dew point control, perform natural gas liquid (NGL)extraction, separate methane and lighter gases from CO₂ and heaviergases, prepare hydrocarbons for LPG production, or condense a refluxstream in deethanizers and/or demethanizers, among others.

Refrigerants

The refrigerants that are utilized according to embodiments describedherein may be mixed refrigerants, where each mixed refrigerant mayinclude two or more single component and/or multicomponent refrigerants.Refrigerants may be imported and stored on-site or, alternatively, someof the components of the refrigerant may be prepared on-site, typicallyby a distillation process integrated with the hydrocarbon processingsystem. In various embodiments, the mixed refrigerants that are utilizedaccording to embodiments described herein include fluorocarbons (FCs),such as HFCs. Exemplary refrigerants are commercially available fromDuPont Corporation, including the ISCEON® family of refrigerants, theSUVA® family of refrigerants, the OPTEON® family of refrigerants, andthe FREON® family of refrigerants.

Multicomponent refrigerants are commercially available. For example,R-401A is a HCFC blend of R-32, R-152a, and R-124. R-404A is a HFC blendof 52 wt. % R-143a, 44 wt. % R-125, and 4 wt. % R-134a. R-406A is ablend of 55 wt. % R-22, 4 wt. % R-600a, and 41 wt. % R-142b. R-407A is aHFC blend of 20 wt. % R-32, 40 wt. % R-125, and 40 wt. % R-134a. R-407Cis a hydrofluorocarbon blend of R-32, R-125, and R-134a. R-408A is aHCFC blend of R-22, R-125, and R-143a. R-409A is a HCFC blend of R-22,R-124, and R-142b. R-410A is a blend of R-32 and R-125. R-500 is a blendof 73.8 wt. % R-12 and 26.2 wt. % of R-152a. R-502 is a blend of R-22and R-115. R-508B is a blend of R-23 and R-116. More specificinformation regarding particular refrigerants that may be used accordingto embodiments described herein is shown below in Table 1.

The ozone depletion potentials for all the refrigerants shown in Table 1are equal to zero. The “Safety Group” shown in Table 1 is an ASHRAEdesignation. A designation of “A” indicates that the OccupationalExposure Limit (OEL) for the refrigerant is above 400 parts per million(ppm). A designation of “B” indicates that the OEL for the refrigerantis below 400 ppm. A number of “1” indicates that the refrigerant isnon-flammable. A number of “2” indicates that the refrigerant isslightly flammable, and a number of “3” indicates that the refrigerantis highly flammable. An “L” suffix indicates that the refrigerant has avery low flame propagation speed.

It is to be understood that the embodiments described herein are notlimited to the use of the refrigerants listed in Table 1. Rather, anyother suitable types of non-flammable refrigerants, or mixtures thereof,may also be used according to embodiments described herein. For example,any suitable types of HFCs, HFOs, and/or inert compounds can be combinedto form a mixed refrigerant according to embodiments described herein.

TABLE 1 Refrigerants Atm. ASHRAE NBP MP Safety Life Number Chemical NameFormula MW ° C. ° C. Group years GWP₁₀₀ R-50 Methane CH₄ 16 −162 −182 A312 25 R-14 Tetrafluoro methane CF₄ 88 −128 −183 A1 50,000 7,390 R-23Trifluoro methane CHF₃ 70 −82 −155 A1 270 14,800 R-41 Fluoro methaneCH₃F 34 −78 −142 A3 2.4 92 R-32 Difluoro methane CH₂F₂ 52 −52 −136 A2L4.9 675 R-218 Octafluoro propane C₃F₈ 188 −37 −148 A1 2,600 8,830R-227ea 1,1,1,2,3,3,3-heptafluoro propane CF₃CFHCF₃ 170 −16 −131 A1 34.23,220 R-245fa 1,1,1,3,3-pentafluoro propane CF₃CH₂CHF₂ 134 15 −102 B17.6 1,030 R-116 Hexafluoro ethane C₂F₆ 138 −78 −101 A1 10,000 12,200R-125 1,1,1,2,2 Pentafluoro ethane C₂HF₅ 120 −49 −103 A1 29 3,500 R-143a1,1,1-trifluoro ethane CH₃CF₃ 84 −48 −111 A2L 52 4,470 R-1234yf2,3,3,3-Tetrafluoropropene C₃H₂F₄ 114 −29 −152 A2L 0.03 0 R-134a1,1,1,2-tetrafluoro ethane CH₂FCF₃ 102 −26 −103 A1 14 1,430 R-152a1,1difluoro ethane CH₂CHF₂ 66 −25 −117 A2 1.4 124 R-1234ze1,3,3,3-Tetrafluoropropene C₃H₂F₄ 114 −19 — A2L — 0 R-C318 Octafluorocyclobutane (—CF₂—)₄ 200 −6 −40 A1 3,200 10,300 R-236fa1,1,1,3,3,3-hexafluoro propane CF₃CH₂CF₃ 152 −2 −96 A1 240 9,810 R-245ca1,1,2,2,3-pentafluoro propane CHF₂CF₂CH₂F 134 25 −82 B1 6.2 693HFE-347mcc Heptafluoropropyl, methyl ether C₃F₇OCH₃ 200 34 −123 — 4.9 0R-728 Nitrogen (non-HFC) N₂ 28 −196 −210 A1 ∞ 0 R-740 Argon (non-HFC) Ar40 −186 −189 A1 ∞ 0 R-784 Krypton (non-HFC) Kr — Xenon (non-HFC) XeR-744 Carbon dioxide (non-HFC) CO₂ 44 −57 −78 A1 33,000 1

According to embodiments described herein, the particular selection offluorocarbons for a mixed refrigerant depends on the desiredrefrigeration temperatures. Natural gas liquefies to form LNG at −162°C. Therefore, in order to produce LNG, a mixed refrigerant that iscapable of chilling natural gas below −162° C. may be selected. In somecases, refrigerants may be used at warmer temperatures, and anotherrefrigeration process, such as an autorefrigeration process, may be usedto aid in the production of LNG.

When selecting a set of fluorocarbons for a mixed refrigerant, thenormal boiling point and the melting point may both be taken intoconsideration. It may be desirable for the temperature of the mixedrefrigerant to be above its freezing point during the entirerefrigeration cycle, so that the refrigerant will not form solids andcause plugging in the system. In addition, it may be desirable to beabove atmospheric pressure during the entire refrigeration cycle toavoid air contamination of the mixed refrigerant. In variousembodiments, the components of the mixed refrigerant are selected suchthat the melting point of each component is below the chillingtemperature. There may be some degree of flexibility in the meltingpoint of the components, since a mixture does not start to freeze at thewarmest pure component melting point. Some melting point depressionoccurs when a high melting point component is diluted in other,non-freezing components and approaches the eutectic point. For example,R-245fa, which has a melting point of −102° C., can be used at lowertemperatures if it is at a sufficiently low concentration in the mixedrefrigerant.

The particular selection of fluorocarbons for a mixed refrigerant mayalso depend on the specific type of refrigeration system for which themixed refrigerant is to be used. For example,

SMR cycles may use mixed refrigerants including a mixture of R-14, R-23,R-32, R-227ea, R-245fa, or the like. Other possible refrigerantcomponents for the mixed refrigerant include R-41, R-218, R-1234yf,R-1234ze, R-152a, and the like. In general, the components of a mixedrefrigerant may be selected such that their NBPs evenly cover thedesired refrigeration range.

In various embodiments, any of a number of different types ofhydrocarbon processing systems can be used with any of the refrigerationsystems described herein. In addition, the refrigeration systemsdescribed herein may utilize any mixture of the refrigerants describedherein.

Refrigeration Systems

Hydrocarbon systems and methods often include refrigeration systems thatutilize mechanical refrigeration, valve expansion, turbine expansion, orthe like. Mechanical refrigeration typically includes compressionsystems and absorption systems, such as ammonia absorption systems.Compression systems are used in the gas processing industry for avariety of processes. For example, compression systems may be used forchilling natural gas for NGL extraction, chilling natural gas forhydrocarbon dew point control, LPG production storage, condensation ofreflux in deethanizers or demethanizers, natural gas liquefaction toproduce LNG, or the like.

FIG. 1 is a process flow diagram of a single stage refrigeration system100. In various embodiments, the single stage refrigeration system 100uses a mixed fluorocarbon refrigerant. The use of a mixed fluorocarbonrefrigerant may allow the single stage refrigeration system 100 tomaintain high efficiency over a wide range of temperatures. Further, invarious embodiments, the single stage refrigeration system 100 isimplemented upstream of a nitrogen refrigeration system or methaneautorefrigeration system including an NRU. Multiple single stagerefrigeration systems 100 may also be implemented in series upstream ofsuch a nitrogen refrigeration system or methane autorefrigerationsystem.

The single stage refrigeration system 100 includes an expansion device102, a chiller 104, a compressor 106, a condenser 108, and anaccumulator 110. The expansion device 102 may be an expansion valve or ahydraulic expander, for example. A saturated liquid refrigerant 112 mayflow from the accumulator 110 to the expansion device 102, and mayexpand across the expansion device 102 isenthalpically. On expansion,some vaporization occurs, creating a chilled refrigerant mixture 114that includes both vapor and liquid. The refrigerant mixture 114 mayenter the chiller 104, also known as the evaporator, at a temperaturelower than the temperature to which a process stream 116, such as anatural gas, is to be cooled. The process stream 116 flows through thechiller 104 and exchanges heat with the refrigerant mixture 114. As theprocess stream 116 exchanges heat with the refrigerant mixture 114, theprocess stream 116 is cooled, while the refrigerant mixture 114vaporizes, creating a saturated vapor refrigerant 118.

After leaving the chiller 104, the saturated vapor refrigerant 118 iscompressed within the compressor 106, and is then flowed into thecondenser 108. Within the condenser 108, the saturated vapor refrigerant118 is converted to a saturated, or slightly sub-cooled, liquidrefrigerant 120. The liquid refrigerant 120 may then be flowed from thecondenser 108 to the accumulator 110. The accumulator 110, which is alsoknown as a surge tank or receiver, may serve as a reservoir for theliquid refrigerant 120. The liquid refrigerant 120 may be stored withinthe accumulator 110 before being expanded across the expansion device102 as the saturated liquid refrigerant 112.

It is to be understood that the process flow diagram of FIG. 1 is notintended to indicate that the single stage refrigeration system 100 isto include all the components shown in FIG. 1. Further, the single stagerefrigeration system 100 may include any number of additional componentsnot shown in FIG. 1, depending on the details of the specificimplementation. For example, in some embodiments, a refrigeration systemcan include two or more compression stages. In addition, therefrigeration system 100 may include an economizer, as discussed furtherwith respect to FIG. 2.

FIG. 2 is a process flow diagram of a two stage refrigeration system 200including an economizer 202. Like numbered items are as described withrespect to FIG. 1. In various embodiments, the two stage refrigerationsystem 200 utilizes a fluorocarbon refrigerant, such as an azeotrope(R-5XX) or a near-azeotrope (R-4XX). Further, in various embodiments,the two stage refrigeration system 200 is implemented upstream of anitrogen refrigeration system or methane autorefrigeration systemincluding an NRU. Multiple two stage refrigeration systems 200 may alsobe implemented in series upstream of such a nitrogen refrigerationsystem or methane autorefrigeration system.

The economizer 202 may be any device or process modification thatdecreases the compressor power usage for a given chiller duty.Conventional economizers 202 include, for example, flash tanks and heatexchange economizers. Heat exchange economizers utilize a number of heatexchangers to transfer heat between process streams. This may reduce theamount of energy input into the two stage refrigeration system 200 byheat integrating process streams with each other.

As shown in FIG. 2, the saturated liquid refrigerant 112 leaving theaccumulator 110 may be expanded across the expansion device 102 to anintermediate pressure at which vapor and liquid may be separated. Forexample, as the saturated liquid refrigerant 112 flashes across theexpansion device 102, a vapor refrigerant 204 and a liquid refrigerant206 are produced at a lower pressure and temperature than the saturatedliquid refrigerant 112. The vapor refrigerant 204 and the liquidrefrigerant 206 may then be flowed into the economizer 202. In variousembodiments, the economizer 202 is a flash tank that effects theseparation of the vapor refrigerant 204 and the liquid refrigerant 206.The vapor refrigerant 204 may be flowed to an intermediate pressurecompressor stage, at which the vapor refrigerant 204 may be combinedwith saturated vapor refrigerant 118 exiting a first compressor 210,creating a mixed saturated vapor refrigerant 208. The mixed saturatedvapor refrigerant 208 may then be flowed into a second compressor 212.

From the economizer 202, the liquid refrigerant 206 may beisenthalpically expanded across a second expansion device 214. Thesecond expansion device 214 may be an expansion valve or a hydraulicexpander, for example. On expansion, some vaporization may occur,creating a refrigerant mixture 216 that includes both vapor and liquid,lowering the temperature and pressure. The refrigerant mixture 216 willhave a higher liquid content than refrigerant mixtures in systemswithout economizers. The higher liquid content may reduce therefrigerant circulation rate and/or reduce the power usage of the firstcompressor 210.

The refrigerant mixture 216 enters the chiller 104, also known as theevaporator, at a temperature lower than the temperature to which theprocess stream 116 is to be cooled. The process stream 116 is cooledwithin the chiller 104, as discussed with respect to FIG. 1. Inaddition, the saturated vapor refrigerant 118 is flowed through thecompressors 210 and 212 and the condenser 108, and the resulting liquidrefrigerant 120 is stored within the accumulator 110, as discussed withrespect to FIG. 1.

It is to be understood that the process flow diagram of FIG. 2 is notintended to indicate that the two stage refrigeration system 200 is toinclude all the components shown in FIG. 2. Further, the two stagerefrigeration system 200 may include any number of additional componentsnot shown in FIG. 2, depending on the details of the specificimplementation. For example, the two stage refrigeration system 200 mayinclude any number of additional economizers or other types of equipmentnot shown in FIG. 2. In addition, the economizer 202 may be a heatexchange economizer rather than a flash tank. The heat exchangeeconomizer may also be used to decrease refrigeration circulation rateand reduce compressor power usage.

In some embodiments, the two stage refrigeration system 200 includesmore than one economizer 202, as well as more than two compressors 210and 212. For example, the two stage refrigeration system 200 may includetwo economizers and three compressors. In general, if the refrigerationsystem 200 includes X number of economizers, the refrigeration system200 will include X +1 number of compressors. Such a refrigeration system200 with multiple economizers may form part of a cascade refrigerationsystem.

FIG. 3 is a process flow diagram of a single stage refrigeration system300 including a heat exchanger economizer 302. Like numbered items areas described with respect to FIG. 1. In various embodiments, the singlestage refrigeration system 300 utilizes a mixed fluorocarbonrefrigerant. Further, in various embodiments, the single stagerefrigeration system 300 is implemented upstream of a nitrogenrefrigeration system or methane autorefrigeration system including anNRU. Multiple single stage refrigeration systems 300 may also beimplemented in series upstream of such a nitrogen refrigeration systemor methane autorefrigeration system.

As shown in FIG. 3, the saturated liquid refrigerant 112 leaving theaccumulator 110 may be expanded across the expansion device 102 to anintermediate pressure at which vapor and liquid may be separated,producing the refrigerant mixture 114. The refrigerant mixture 114 maybe flowed into the chiller 104 at a temperature lower than thetemperature to which the process stream 116 is to be cooled. The processstream 116 may be cooled within the chiller 104, as discussed withrespect to FIG. 1.

From the chiller 104, the saturated vapor refrigerant 118 may be flowedthrough the heat exchanger economizer 302. The cold, low-pressuresaturated vapor refrigerant 118 may be used to subcool the saturatedliquid refrigerant 112 within the heat exchanger economizer 302. Thesuperheated vapor refrigerant 304 exiting the heat exchanger economizer302 may then be flowed through the compressor 106 and the condenser 108,and the resulting liquid refrigerant 120 may be stored within theaccumulator 110, as discussed with respect to FIG. 1.

It is to be understood that the process flow diagram of FIG. 3 is notintended to indicate that the single stage refrigeration system 300 isto include all the components shown in FIG. 3. Further, the single stagerefrigeration system 300 may include any number of additional componentsnot shown in FIG. 3, depending on the details of the specificimplementation.

FIG. 4 is a process flow diagram of an LNG production system 400. Asshown in FIG. 4, LNG 402 may be produced from a natural gas stream 404using a number of different refrigeration systems. As shown in FIG. 4, aportion of the natural gas stream 404 may be separated from the naturalgas stream 404 prior to entry into the LNG production system 400, andmay be used as a fuel gas stream 406. The remaining natural gas stream404 may be flowed into an initial natural gas processing system 408.Within the natural gas processing system 408, the natural gas stream 404may be purified and cooled. For example, the natural gas stream 404 maybe cooled using a first mixed fluorocarbon refrigerant 410, a secondmixed fluorocarbon refrigerant 412, and a high-pressure nitrogenrefrigerant 414. The cooling of the natural gas stream 404 may result inthe production of the LNG 402. In some embodiments, the broadertemperature range of a mixed refrigerant system will make it possible touse a single mixed refrigerant for both the first mixed fluorocarbonrefrigerant 410 and the second mixed fluorocarbon refrigerant 412.

Within the LNG production system 400, heavy hydrocarbons 416 may beremoved from the natural gas stream 406, and a portion of the heavyhydrocarbons 416 may be used to produce gasoline 418 within a heavyhydrocarbon processing system 420. In addition, any residual natural gas422 that is separated from the heavy hydrocarbons 416 during theproduction of the gasoline 418 may be returned to the natural gas stream404.

The produced LNG 402 may include some amount of nitrogen 424. Therefore,the LNG 402 may be flowed through an NRU 426. The NRU 426 separates thenitrogen 424 from the LNG 402, producing the final LNG product.

It is to be understood that the process flow diagram of FIG. 4 is notintended to indicate that the LNG production system 400 is to includeall the components shown in FIG. 4. Further, the LNG production system400 may include any number of additional components not shown in FIG. 4or different locations for the fluorocarbon refrigerant chillers withinthe process, depending on the details of the specific implementation.For example, any number of alternative refrigeration systems may also beused to produce the LNG 402 from the natural gas stream 404. Inaddition, any number of different refrigeration systems may be used incombination to produce the LNG 402.

Hydrocarbon Processing Systems for the Production of LNG

According to embodiments described herein, LNG may be produced within ahydrocarbon processing system using mixed fluorocarbon refrigerants. Insome embodiments, the fluorocarbon components within the mixedfluorocarbon refrigerants are non-flammable, non-toxic, andnon-reactive. The fluorocarbon components for a particular mixedfluorocarbon refrigerant may be selected such that the cooling curve ofthe mixed fluorocarbon refrigerant closely matches the cooling curve ofthe LNG being chilled. Matching the cooling curve of the mixedfluorocarbon refrigerant to the cooling curve of the LNG may increasethe performance and efficiency of the hydrocarbon processing system.

FIG. 5 is a process flow diagram of a hydrocarbon processing system 500including an SMR cycle 502. The SMR cycle 502 may cool a feed gas 504 toproduce LNG 506 using a mixed fluorocarbon refrigerant 508. Thehydrocarbon processing system 500 also includes a low pressure NRU 510,which may be used to purify the LNG 506 by separating the LNG 506 from afuel stream 512 including nitrogen.

The SMR cycle 502 includes a heat exchanger 514, a compressor 516, acondenser 518, and an expansion device 520. The expansion device 520 maybe an expansion valve or a hydraulic expander, for example. The mixedfluorocarbon refrigerant 508 is flowed from the condenser 518 to theheat exchanger 514. Within the heat exchanger 514, the mixedfluorocarbon refrigerant 508 cools the feed gas 504 to produce the LNG506 via indirect heat exchange.

From the heat exchanger 514, the mixed fluorocarbon refrigerant 508 isflowed to the expansion device 520, and is expanded across the expansiondevice 520 isenthalpically. On expansion, some vaporization occurs,creating a chilled mixed fluorocarbon refrigerant 522 that includes bothvapor and liquid. The chilled mixed fluorocarbon refrigerant 522 isflowed back to the heat exchanger 514 and is used to aid in the coolingof the feed gas 508 within the heat exchanger 514. As the feed gas 508exchanges heat with the chilled mixed fluorocarbon refrigerant 522, thechilled mixed fluorocarbon refrigerant 522 vaporizes, creating a vapormixed fluorocarbon refrigerant 524.

The vapor mixed fluorocarbon refrigerant 524 is then compressed withinthe compressor 516 and flowed into the condenser 518. Within thecondenser 518, the vapor mixed fluorocarbon refrigerant 524 is convertedto a saturated, or slightly sub-cooled, liquid mixed fluorocarbonrefrigerant 508. The liquid mixed fluorocarbon refrigerant 508 is thenflowed back into the heat exchanger 514.

In various embodiments, the LNG 506 that is produced via the SMR cycle502 includes some amount of impurities, such as nitrogen. Therefore, theLNG 506 is flowed to into the NRU 510. The NRU 510 separates the fuelstream 512 including the nitrogen from the LNG 506, producing the finalLNG product. The final LNG product may then be flowed from thehydrocarbon processing system 500 to a desired destination using a pump526.

It is to be understood that the process flow diagram of FIG. 5 is notintended to indicate that the hydrocarbon processing system 500 is toinclude all the components shown in FIG. 5. Further, the hydrocarbonprocessing system 500 may include any number of additional componentsnot shown in FIG. 5, depending on the details of the specificimplementation.

FIG. 6 is a process flow diagram of the hydrocarbon processing system500 of FIG. 5 with the addition of a nitrogen refrigeration system 600.Like numbered items are as described with respect to FIG. 5. Accordingto the embodiment shown in FIG. 6, the SMR cycle 502 may be operated ata higher temperature. Therefore, the output of the SMR cycle 502 may becooled feed gas 504, rather than LNG 506, or may be a mixture of cooledfeed gas 504 and LNG 506.

From the SMR cycle 502, the feed gas 504 is flowed into the nitrogenrefrigeration system 600. Within the nitrogen refrigeration system 600,the feed gas may be cooled to produce the LNG 506 via indirect heatexchange with a nitrogen refrigerant 602 within a first heat exchanger604. The LNG 506 is then flowed into the NRU 510, as discussed withrespect to FIG. 5.

The nitrogen refrigeration system 600 includes the first heat exchanger604, a second heat exchanger 606, a compressor 608, a condenser 610, andan expander 612. From the first heat exchanger 604, the nitrogenrefrigerant 602 is flowed through the second heat exchanger 606. Withinthe second heat exchanger 606, the nitrogen refrigerant 602 is cooledvia indirect heat exchange with a chilled, vapor nitrogen refrigerant614. The nitrogen refrigerant 602 is then compressed within thecompressor 608 and flowed into the condenser 610.

Within the condenser 610, the nitrogen refrigerant 602 is converted tothe vapor nitrogen refrigerant 614. The vapor nitrogen refrigerant 614is flowed through the second heat exchanger 606, in which the vapornitrogen refrigerant 614 exchanges heat with the warmer nitrogenrefrigerant 602 exiting the first heat exchanger 604.

The chilled, vapor nitrogen refrigerant 614 is then flowed through theexpander 612. The expander 612 expands the vapor nitrogen refrigerant614 to a low pressure with a corresponding reduction in temperature. Theresulting cold nitrogen refrigerant 602 is flowed through the first heatexchanger 604 to exchange heat with the feed gas 504.

It is to be understood that the process flow diagram of FIG. 6 is notintended to indicate that the hydrocarbon processing system 600 is toinclude all the components shown in FIG. 6. Further, the hydrocarbonprocessing system 600 may include any number of additional componentsnot shown in FIG. 6, depending on the details of the specificimplementation.

FIG. 7 is a process flow diagram of the hydrocarbon processing system500 of FIG. 5 with the addition of a methane autorefrigeration system700. Like numbered items are as described with respect to FIG. 5.According to the embodiment shown in FIG. 7, the SMR cycle 502 may beoperated at a higher temperature. Therefore, the output of the SMR cycle502 may be cooled feed gas 504, rather than LNG 506, or may be a mixtureof cooled feed gas 504 and LNG 506.

From the SMR cycle 502, the cooled feed gas 504 is flowed into the NRU510. The NRU 510 purifies the feed gas 504, producing an LNG bottomsstream 702 and a fuel gas overhead stream 704. The LNG bottoms stream702 is flowed through an expansion device 706, such as an expansionvalve or hydraulic expander, and into a heat exchanger 708. Within theheat exchanger 708, the LNG bottoms stream 702 exchanges heat with theoverhead fuel stream 704, cooling the overhead fuel stream 704 andproducing a mixed fuel stream 710 including both the vapor fuel stream512 and a liquid fuel stream 712.

The mixed fuel stream 710 is then flowed into a flash drum 714. Theflash drum 714 separates the vapor fuel stream 512 from the liquid fuelstream 712. The liquid fuel stream 712 may then be flowed back into theNRU 510 as reflux.

As the LNG bottoms stream 702 exchanges heat with the overhead fuelstream 704 within the heat exchanger 708, it may be partially vaporized,producing a mixed phase feed stream 716. From the heat exchanger 708,the mixed phase feed stream 716 is flowed into a first flash drum 718within the methane autorefrigeration system 700.

The first flash drum 718 separates the mixed phase feed stream 716 intoa vapor stream 720 that includes primarily natural gas and an LNG stream722. The vapor stream 720 is flowed into a first compressor 724. Fromthe first compressor 724, the resulting natural gas stream 726 may becombined with the initial feed gas 504 prior to entry of the feed gas504 into the SMR cycle 502.

From the first flash drum 718, the LNG stream 722 is flowed through anexpansion device 728, such as an expansion valve or hydraulic expander,which may control the flow of the LNG stream 728 into a second flashdrum 730. Specifically, the expansion device 728 may allow a portion ofthe liquid from the LNG stream 722 to flash, creating a mixed phasestream that is flowed into the second flash drum 730.

The second flash drum 730 separates the mixed phase stream into thefinal LNG product 506 and a vapor stream 732 that includes primarilynatural gas. The vapor stream 732 is flowed into a second compressor734. From the second compressor 734, the vapor stream 732 is combinedwith the vapor stream 720 from the first flash drum 718 prior to entryof the vapor stream 720 into the first compressor 724. Furthermore, fromthe second flash drum 730, the final LNG product 506 may be flowed to adesired destination using the pump 526.

It is to be understood that the process flow diagram of FIG. 7 is notintended to indicate that the hydrocarbon processing system 700 is toinclude all the components shown in FIG. 7. Further, the hydrocarbonprocessing system 700 may include any number of additional componentsnot shown in FIG. 7, depending on the details of the specificimplementation.

FIG. 8 is a process flow diagram of a hydrocarbon processing system 800including a pre-cooled SMR cycle 802. The pre-cooled SMR cycle 802 maycool a feed gas 804 to produce LNG 806 using a mixed fluorocarbonrefrigerant 808. The hydrocarbon processing system 800 also includes alow pressure NRU 810, which may be used to purify the LNG 806 byseparating the LNG 806 from a fuel stream 812 including nitrogen.

Within the pre-cooled SMR cycle 802, the incoming feed gas 804 ispre-cooled and partially condensed in a first chiller 814 via indirectheat exchange with a fluorocarbon refrigerant. For example, the feed gas804 may be cooled in the first chiller 814 using a refrigerant blendsuch as R-410a or R-404a, or using a pure component refrigerant such asR-125, R-32, or R-218.

The chilled feed gas 816 is then flowed into a main cryogenic heatexchanger 818. Within the main cryogenic heat exchanger 818, the feedgas 816 is cooled to produce the LNG 806 via indirect heat exchange withthe mixed fluorocarbon refrigerant 808. The main cryogenic heatexchanger 818 may include a number of small-diameter, spiral-wound tubebundles 820, which may permit very close temperature matches between thechilled feed gas 816 and the mixed fluorocarbon refrigerant 808.

After the mixed fluorocarbon refrigerant 808 flows through the maincryogenic heat exchanger 818, the mixed fluorocarbon refrigerant 808 isexpanded across an expansion device 822, such as an expansion valve orhydraulic expander. On expansion, some vaporization occurs, creating achilled mixed fluorocarbon refrigerant 824 that includes both vapor andliquid. The chilled mixed fluorocarbon refrigerant 824 is then sprayedinto the main cryogenic heat exchanger 818 via a number of spray nozzles826. In various embodiments, spraying the chilled mixed fluorocarbonrefrigerant 824 into the main cryogenic heat exchanger 818 provides foradditional cooling of the feed gas 816 and the mixed fluorocarbonrefrigerant 808 flowing through the tube bundles 820.

The chilled mixed fluorocarbon refrigerant 824 is then flowed out of themain cryogenic heat exchanger 818 as a bottoms stream 828. The bottomsstream 828 is compressed in a compressor 830, producing a compressedmixed fluorocarbon refrigerant 832. The compressed mixed fluorocarbonrefrigerant 832 is chilled and partially condensed within a secondchiller 834 and a third chiller 836. The resulting chilled mixedfluorocarbon refrigerant 838 is flowed into a flash drum 839, whichseparates the chilled mixed fluorocarbon refrigerant 838 into a vaporstream and a liquid stream. The vapor stream is flowed into the maincryogenic heat exchanger 818 as the mixed fluorocarbon refrigerant 808,and the liquid stream is flowed into the main cryogenic heat exchanger818 as an additional mixed fluorocarbon refrigerant 840. The additionalmixed fluorocarbon refrigerant 840 may provide cooling for the mixedfluorocarbon refrigerant 808 via indirect heat exchange with the mixedfluorocarbon refrigerant 808.

Upon exiting the main cryogenic heat exchanger 818, the additional mixedfluorocarbon refrigerant 840 is expanded across an expansion device 842,such as an expansion valve or hydraulic expander. On expansion, somevaporization occurs, creating a chilled mixed fluorocarbon refrigerant844 that includes both vapor and liquid. The chilled mixed fluorocarbonrefrigerant 844 is then sprayed into the main cryogenic heat exchanger818 via a number of additional spray nozzles 846. After flowing throughthe main cryogenic heat exchanger 818, the chilled mixed fluorocarbonrefrigerant 844 is flowed out of the main cryogenic heat exchanger 818along with the bottoms stream 828.

From the main cryogenic heat exchanger 818, the produced LNG 806 isflowed through an expansion device 848, such as an expansion valve orhydraulic expander, and into the NRU 810. The NRU 810 separates the fuelstream 812 from the LNG 806, producing the final LNG product. The finalLNG product may then be flowed from the hydrocarbon processing system800 to a desired destination using a pump 850.

It is to be understood that the process flow diagram of FIG. 8 is notintended to indicate that the hydrocarbon processing system 800 is toinclude all the components shown in FIG. 8. Further, the hydrocarbonprocessing system 800 may include any number of additional componentsnot shown in FIG. 8, depending on the details of the specificimplementation. In some embodiments, the mixed fluorocarbon refrigerant808 used in the main cryogenic heat exchanger 818 of FIG. 8 includesnitrogen, e.g., R-728, and/or argon, e.g., R-740, in addition to one ormore fluorocarbon refrigerant components.

FIG. 9 is a process flow diagram of a hydrocarbon processing system 900including a DMR cycle 902. The DMR cycle 902 may include a warm MR cycleand a cold MR cycle connected in series. The DMR cycle 902 may be usedto cool a feed gas 904 to produce LNG 906 using a first mixedfluorocarbon refrigerant 908 within the warm MR cycle and a second mixedfluorocarbon refrigerant 910 within the cold MR cycle. The hydrocarbonprocessing system 900 also includes a low pressure NRU 912, which may beused to purify the LNG 906 by separating the LNG 906 from a fuel stream914 including nitrogen.

In some embodiments, the first mixed fluorocarbon refrigerant 908 withinthe warm MR cycle includes R-32, R-152a, R-245fa, R-227ea, HFE-347mcc,and/or other high boiling components. In addition, in some embodiments,the second mixed fluorocarbon refrigerant 910 within the cold MR cycleincludes R-14, R-170, R-41, xenon, R-23, R-116, R-1150, R-50, R-784,and/or other low boiling components.

Within the hydrocarbon processing system 900, the feed gas 904 is cooledto produce the LNG 906 using a first heat exchanger 916 and a secondheat exchanger 918. The feed gas 904 is cooled within the first heatexchanger 916 via indirect heat exchange along with the first mixedfluorocarbon refrigerant 908 and the second mixed fluorocarbonrefrigerant 910.

From the first heat exchanger 916, the first mixed fluorocarbonrefrigerant 908 is flowed to an expansion device 920, such as anexpansion valve or hydraulic expander, and is expanded across theexpansion device 920 isenthalpically. On expansion, some vaporizationoccurs, creating a chilled mixed fluorocarbon refrigerant 922 thatincludes both vapor and liquid. The chilled mixed fluorocarbonrefrigerant 922 is flowed back to the first heat exchanger 916 and isused to cool the first mixed fluorocarbon refrigerant 908, the secondmixed fluorocarbon refrigerant 910, and the feed gas 904 within thefirst heat exchanger 916. As the first mixed fluorocarbon refrigerant908, the second mixed fluorocarbon refrigerant 910, and the feed gas 904exchange heat with the chilled mixed fluorocarbon refrigerant 922, thechilled mixed fluorocarbon refrigerant 922 vaporizes, creating a vapormixed fluorocarbon refrigerant 924.

The vapor mixed fluorocarbon refrigerant 924 is then compressed within acompressor 926 and condensed within a condenser 928. The condensed mixedfluorocarbon refrigerant is then flowed back into the first heatexchanger 916 as the first mixed fluorocarbon refrigerant 908.

From the first heat exchanger 916, the second mixed fluorocarbonrefrigerant 910 is flowed into the second heat exchanger 918. Within thesecond heat exchanger 918, the second mixed fluorocarbon refrigerant 910is further cooled along with the feed gas 904, producing the LNG 906.

Upon exiting the second heat exchanger 918, the second mixedfluorocarbon refrigerant 910 is flowed to an expansion device 930, suchas an expansion valve or hydraulic expander, and is expanded across theexpansion device 930 isenthalpically. On expansion, some vaporizationoccurs, creating a chilled mixed fluorocarbon refrigerant 932 thatincludes both vapor and liquid. The chilled mixed fluorocarbonrefrigerant 932 is flowed back to the second heat exchanger 918 and isused to cool both the feed gas 904 and the second mixed fluorocarbonrefrigerant 910 within the second heat exchanger 918. As the feed gas904 exchanges heat with the chilled mixed fluorocarbon refrigerant 932,the chilled mixed fluorocarbon refrigerant 932 vaporizes, creating avapor mixed fluorocarbon refrigerant 934.

The vapor mixed fluorocarbon refrigerant 934 is then compressed within acompressor 936, and cooled within a heat exchanger 938. The condensedmixed fluorocarbon refrigerant is flowed back into the first heatexchanger 916 as the second mixed fluorocarbon refrigerant 910.

In various embodiments, the LNG 906 that is produced via the DMR cycle902 includes some amount of impurities, such as nitrogen. Therefore, theLNG 906 is flowed to into the NRU 912. The NRU 912 separates the fuelstream 914 from the LNG 906, producing the final LNG product. The finalLNG product may be flowed from the hydrocarbon processing system 900 toa desired destination using a pump 940.

It is to be understood that the process flow diagram of FIG. 9 is notintended to indicate that the hydrocarbon processing system 900 is toinclude all the components shown in FIG. 9. Further, the hydrocarbonprocessing system 900 may include any number of additional componentsnot shown in FIG. 9, depending on the details of the specificimplementation.

FIGS. 10A and 10B are process flow diagrams of a hydrocarbon processingsystem 1000 including an SMR cycle 1002, an NRU 1004, and a methaneautorefrigeration system 1006. In various embodiments, the hydrocarbonprocessing system 1000 is used to produce LNG 1008 from a natural gasstream 1010.

As shown in FIG. 10A, the natural gas stream 1010 is flowed into a pipejoint 1012 within the hydrocarbon processing system 1000. The pipe joint1012 combines the natural gas stream 1010 with another natural gasstream. The combined natural gas stream is compressed within a firstcompressor 1014 and flowed into another pipe joint 1016 via line 1018.

The pipe joint 1016 splits the natural gas stream into two separatenatural gas streams. A first natural gas stream is combined with anothernatural gas stream via a pipe joint 1020 and then flowed out of thehydrocarbon processing system 1000 as fuel 1022. A second natural gasstream is chilled within a first chiller 1024 and flowed into anotherpipe joint 1026. The pipe joint 1026 splits the natural gas stream intotwo separate natural gas streams. A first natural gas stream is flowedinto a first heat exchanger 1028 within the SMR cycle 1002 via line1030. A second natural gas stream is flowed into a second heat exchanger1032 via line 1034.

Within the first heat exchanger 1028, the natural gas stream is cooledvia indirect heat exchange with a circulating mixed fluorocarbonrefrigerant stream. From the first heat exchanger 1028, the mixedfluorocarbon refrigerant stream is flowed to an expansion device 1036,such as an expansion valve or hydraulic expander, via line 1038, and isexpanded across the expansion device 1036 isenthalpically. On expansion,some vaporization occurs, creating a chilled mixed fluorocarbonrefrigerant stream that includes both vapor and liquid. The chilledmixed fluorocarbon refrigerant stream is flowed back to the first heatexchanger 1028 and is used to aid in the cooling of the natural gasstream within the first heat exchanger 1028. As the natural gas streamexchanges heat with the chilled mixed fluorocarbon refrigerant stream,the chilled mixed fluorocarbon refrigerant stream vaporizes, creating avapor mixed fluorocarbon refrigerant stream.

The vapor mixed fluorocarbon refrigerant is then compressed within asecond compressor 1040 and partially condensed within a second chiller1042. The condensed mixed fluorocarbon refrigerant is then flowed into afirst flash drum 1044 via line 1046. The flash drum separates thepartially condensed mixed fluorocarbon refrigerant stream into a vapormixed fluorocarbon refrigerant stream and a liquid mixed fluorocarbonrefrigerant. The vapor mixed fluorocarbon refrigerant stream iscompressed within a third compressor 1048 and flowed into a pipe joint1050. The liquid mixed fluorocarbon refrigerant stream is pumped intothe pipe joint 1050 via a pump 1052.

Within the pipe joint 1050, the vapor and liquid mixed fluorocarbonrefrigerant streams are recombined. The recombined mixed fluorocarbonrefrigerant stream is further cooled within a third chiller 1053 andflowed back into the first heat exchanger 1028. Within the first heatexchanger 1028, the recombined mixed fluorocarbon refrigerant stream isfully condensed and sub-cooled, and is then flowed back to the expansiondevice 1036 via line 1038.

From the first heat exchanger 1028, the resulting LNG stream is flowedinto a pipe joint 1054, in which it is combined with an LNG stream fromthe second heat exchanger 1032. The combined LNG stream is then flowedinto the NRU 1004 via line 1056 to remove excess nitrogen from the LNGstream. Specifically, the LNG stream is flowed into a reboiler 1058,which decreases the temperature of the LNG stream. The cooled LNG streammay be expanded within a hydraulic expansion turbine 1060 and flowedthrough an expansion device 1062, such as an expansion valve orhydraulic expander, which lowers the temperature and pressure of the LNGstream.

The LNG stream is flowed into a cryogenic fractionation column 1064,such as an NRU tower, within the NRU 1004. In addition, heat istransferred to the cryogenic fractionation column 1064 from the reboiler1058 via line 1066. The cryogenic fractionation column 1064 separatesnitrogen from the LNG stream via a cryogenic distillation process. Anoverhead stream is flowed out of the cryogenic fractionation column 1064via line 1068. The overhead stream may include primarily methane,nitrogen, and other low boiling point or non-condensable gases, such ashelium, which have been separated from the LNG stream.

The overhead stream is flowed into a reflux condenser 1070 via line1068. Within the reflux condenser 1070, the overhead stream is cooledvia indirect heat exchange with an LNG stream. The heated overheadstream is then flowed into a reflux separator 1072. The reflux separator1072 separates any liquid within the overhead stream and returns theliquid to the cryogenic fractionation column 1064 as reflux. Theseparation of the liquid from the overhead stream via the refluxseparator 1072 results in the production of a vapor stream. The vaporstream may be a fuel stream including primarily nitrogen and other lowboiling point gases. From the reflux separator 1072, the vapor stream isflowed through the second heat exchanger 1032 via line 1074. The vaporstream is compressed within a fourth compressor 1076, chilled within afourth chiller 1078, further compressed within a fifth compressor 180,and further chilled within a fifth chiller 1082. The fuel stream is thencombined with the other natural gas stream within the pipe joint 1020and flowed out of the hydrocarbon processing system 1000 as fuel 1022.

The bottoms stream that is produced within the cryogenic fractionationcolumn 1064 includes primarily LNG with traces of nitrogen. The LNGstream is flowed into the reflux condenser 1070 and is used to cool theoverhead stream from the cryogenic fractionation column 1064. As the LNGstream exchanges heat with overhead stream, it is partially vaporized,producing a multiphase natural gas stream.

The multiphase natural gas stream is flowed into a second flash drum1084 via line 1083. The second flash drum 1084 separates the multiphasenatural gas stream into a natural gas stream and an LNG stream. Thenatural gas stream is combined within another natural gas stream withina pipe joint 1086, compressed within a sixth compressor 1087, andcombined with the initial natural gas stream 1010 within the pipe joint1012.

From the second flash drum 1084, the LNG stream is flowed through anexpansion device 1088, such as an expansion valve or hydraulic expander,that controls the flow of the natural gas stream into a third flash drum1089. The expansion device 1088 reduces the temperature and pressure ofthe natural gas stream, resulting in the flash evaporation of thenatural gas stream into both a natural gas stream and an LNG stream. Thenatural gas stream is then separated from the LNG steam via the thirdflash drum 1089.

The natural gas stream is flowed from the third flash drum 1089 into apipe joint 1090, in which the natural gas stream is combined withanother natural gas stream. The combined natural gas stream iscompressed within a seventh compressor 1091 and then flowed into thepipe joint 1086.

From the third flash drum 1089, the LNG stream is flowed through anexpansion device 1092, such as an expansion valve or hydraulic expander,that controls the flow of the natural gas stream into a fourth flashdrum 1093. The expansion device 1092 reduces the temperature andpressure of the natural gas stream, resulting in the flash evaporationof the natural gas stream into both a natural gas stream and an LNGstream. The natural gas stream is then separated from the LNG steam viathe fourth flash drum 1093.

The natural gas stream is flowed from the fourth flash drum 1093 into apipe joint 1094, in which the natural gas stream is combined withanother natural gas stream. The combined natural gas stream iscompressed within an eighth compressor 1095 and flowed into the pipejoint 1090.

The LNG stream is flowed into an LNG tank 1096. The LNG tank 1096 maystore the LNG stream for any period of time. Boil-off gas generatedwithin the LNG tank 1096 is flowed to the pipe joint 1094 and combinedwithin the natural gas stream from the fourth flash drum 1093. At anypoint in time, the final LNG stream 1008 may be transported to a LNGtanker 1097 using a pump 1098, for transport to markets. Additionalboil-off gas 1099 generated while loading the final LNG stream 1008 intothe LNG tanker 1097 may be recovered in the hydrocarbon processingsystem 1000.

It is to be understood that the process flow diagrams of FIGS. 10A and10B are not intended to indicate that the hydrocarbon processing system1000 is to include all the components shown in FIGS. 10A and 10B.Further, the hydrocarbon processing system 1000 may include any numberof additional components not shown in FIGS. 10A and 10B, depending onthe details of the specific implementation.

FIGS. 11A and 11B are process flow diagrams of a hydrocarbon processingsystem 1100 including an economized DMR cycle 1102, an NRU 1104, and amethane autorefrigeration system 1106. In various embodiments, thehydrocarbon processing system 1100 is used to produce LNG 1108 from anatural gas stream 1110.

As shown in FIG. 11A, the natural gas stream 1110 is flowed into a pipejoint 1112 within the hydrocarbon processing system 1100. The pipe joint1112 splits the natural gas stream 110 into three separate natural gasstreams. A first natural gas stream is flowed to a pipe joint 1114 vialine 1116. Within the pipe joint 1114, the first natural gas stream iscombined with another stream including natural gas, and the combinedstream is flowed out of the hydrocarbon processing system 1100 as fuel1118.

From the pipe joint 1112, a second natural gas stream is flowed into theNRU 1104. Within the NRU 1104, the natural gas stream is cooled within afirst heat exchanger 1120 and combined with an LNG stream exiting theeconomized DMR cycle 1102 within a pipe joint 1122.

Furthermore, a third natural gas stream is flowed from the pipe joint1112 to another pipe joint 1124 as the main feed stream. Within the pipejoint 1124, the natural gas stream is combined with another natural gasstream from the methane autorefrigeration system 1106. The combinednatural gas stream is then cooled within the economized DMR cycle 1102.Specifically, the natural gas stream is cooled using a second heatexchanger 1126, a third heat exchanger 1128, and a fourth heat exchanger1130 within a warm MR cycle of the economized DMR cycle 1102. Thenatural gas stream is further cooled using a fifth heat exchanger 1132and a sixth heat exchanger 1134 within a cold MR cycle of the economizedDMR cycle 1102.

Within the second heat exchanger 1126, the natural gas stream is cooledvia indirect heat exchange with a circulating warm fluorocarbonrefrigerant stream. From the second heat exchanger 1126, the warmfluorocarbon refrigerant stream is flowed into a pipe joint 1140, inwhich it is combined with another warm fluorocarbon refrigerant streamfrom the third and fourth heat exchangers 1128 and 1130.

From the pipe joint 1140, the warm fluorocarbon refrigerant stream iscompressed within a compressor 1142 and chilled within a chiller 1144.The warm fluorocarbon refrigerant stream is then flowed through thesecond heat exchanger 1126. Within the second heat exchanger 1126, thewarm fluorocarbon refrigerant stream is sub-cooled via indirect heatexchange. From the second heat exchanger 1126, the sub-cooledfluorocarbon refrigerant stream is flowed to a pipe joint 1148, whichsplits the fluorocarbon refrigerant stream into two fluorocarbonrefrigerant streams. A first fluorocarbon refrigerant stream is flowedthrough an expansion device 1150 and back into the second heat exchanger1126. Within the second heat exchanger 1126, the fluorocarbonrefrigerant stream cools the natural gas stream and the otherfluorocarbon refrigerant streams flowing through the second heatexchanger 1126. The fluorocarbon refrigerant stream is then flowed intothe pipe joint 1140.

A second fluorocarbon refrigerant stream is flowed from the pipe joint1150 into the third heat exchanger 1128 via line 1152. Within the thirdheat exchanger 1128, the fluorocarbon refrigerant stream is furtherchilled and sub-cooled via indirect heat exchange. From the third heatexchanger 1128, the sub-cooled fluorocarbon refrigerant stream is flowedto a pipe joint 1153, which splits the fluorocarbon refrigerant streaminto two fluorocarbon refrigerant streams. A first fluorocarbonrefrigerant stream is flowed through an expansion device 1154 and backinto the third heat exchanger 1128. Within the third heat exchanger1128, the fluorocarbon refrigerant stream cools the natural gas streamand the other fluorocarbon refrigerant streams flowing through the thirdheat exchanger 1128. The fluorocarbon refrigerant stream is then flowedinto a pipe joint 1156, in which it is combined with another warmfluorocarbon refrigerant stream from the fourth heat exchanger 1130.From the pipe joint 1156, the combined warm fluorocarbon refrigerantstream is compressed within a compressor 1158, chilled within a chiller1159, and flowed into the pipe joint 1140 to be combined with thefluorocarbon refrigerant stream exiting the second heat exchanger 1126.

A second fluorocarbon refrigerant stream is flowed from the pipe joint1153 into the fourth heat exchanger 1130 via line 1160. Within thefourth heat exchanger 1130, the fluorocarbon refrigerant stream isfurther chilled and sub-cooled via indirect heat exchange. From thefourth heat exchanger 1130, the sub-cooled fluorocarbon refrigerantstream is flowed through an expansion device 1161 and back into thefourth heat exchanger 1130. Within the fourth heat exchanger 1130, thefluorocarbon refrigerant stream cools the natural gas stream and theother fluorocarbon refrigerant streams flowing through the fourth heatexchanger 1130. The fluorocarbon refrigerant stream is then compressedwithin a compressor 1163 and flowed into the pipe joint 1156 to becombined with the fluorocarbon refrigerant stream exiting the third heatexchanger 1128.

In various embodiments, a fluorocarbon refrigerant stream from the coldMR cycle of the economized DMR cycle 1102 is flowed through the secondheat exchanger 1126, the third heat exchanger 1128, and the fourth heatexchanger 1130 within the warm MR cycle via line 1164. Within the secondheat exchanger 1126, the third heat exchanger 1128, and the fourth heatexchanger 1130, the fluorocarbon refrigerant stream from the cold MRcycle is cooled and condensed via indirect heat exchange with thefluorocarbon refrigerant within the warm MR cycle. The cold, liquidfluorocarbon refrigerant stream exiting the fourth heat exchanger 1130is flowed into the fifth heat exchanger 1132 of the cold MR cycle vialine 1165.

Within the fifth heat exchanger 1132, the cold fluorocarbon refrigerantstream is further sub-cooled via indirect heat exchange. From the fifthheat exchanger 1132, the sub-cooled fluorocarbon refrigerant stream isflowed to a pipe joint 1166, which splits the fluorocarbon refrigerantstream into two fluorocarbon refrigerant streams. A first fluorocarbonrefrigerant stream is flowed through an expansion device 1167 and backinto the fifth heat exchanger 1132. Within the fifth heat exchanger1132, the fluorocarbon refrigerant stream cools the natural gas streamand the incoming liquid fluorocarbon refrigerant stream 1165. Thefluorocarbon refrigerant stream is then flowed into a pipe joint 1168,in which it is combined with a fluorocarbon refrigerant stream from thesixth heat exchanger 1134. The combined fluorocarbon refrigerant streamis compressed within a compressor 1169, chilled within a chiller 1170,and flowed back into the warm MR cycle of economized DMR cycle 1102 vialine 1164.

A second fluorocarbon refrigerant stream is flowed from the pipe joint1166 into the sixth heat exchanger 1134 via line 1171. Within the sixthheat exchanger 1134, the fluorocarbon refrigerant stream is furtherchilled and sub-cooled via indirect heat exchange. From the sixth heatexchanger 1134, the fluorocarbon refrigerant stream is flowed through anexpansion valve 1172 and back into the sixth heat exchanger 1134. Withinthe sixth heat exchanger 1134, the fluorocarbon refrigerant stream coolsthe natural gas stream, producing an LNG stream, and chills the liquidfluorocarbon refrigerant stream. The fluorocarbon refrigerant stream isthen compressed within a compressor 1173 and flowed into the pipe joint1168, in which it is combined with the fluorocarbon refrigerant streamexiting the fifth heat exchanger 1132.

From the sixth heat exchanger 1134, the resulting LNG stream is flowedout of the economized DMR cycle 1102 and into the NRU 1104 via line1174. Specifically, the LNG stream is flowed into the pipe joint 1122,in which it is combined with the natural gas stream exiting the firstheat exchanger 1120. The LNG stream is then flowed into a reboiler 1175,which decreases the temperature of the LNG stream. The cooled LNG streammay be expanded within a hydraulic expansion turbine 1176 and flowedthrough an expansion device 1177, such as an expansion valve orhydraulic expander, which lowers the temperature and pressure of the LNGstream.

The LNG stream is flowed into a cryogenic fractionation column 1178,such as an NRU tower, within the NRU 1104. In addition, heat istransferred to the cryogenic fractionation column 1178 from the reboiler1175 via line 1179. The cryogenic fractionation column 1178 separatesnitrogen from the LNG stream via a cryogenic distillation process. Anoverhead stream is flowed out of the cryogenic fractionation column 1178via line 1180. The overhead stream may include primarily methane,nitrogen, and other low boiling point or non-condensable gases, such ashelium, which have been separated from the LNG stream.

The overhead stream is flowed into a reflux condenser 1181. Within thereflux condenser 1181, the overhead stream is cooled via indirect heatexchange with an LNG stream. The heated overhead stream is then flowedinto a reflux separator 1182. The reflux separator 1182 separates anyliquid within the overhead stream and returns the liquid to thecryogenic fractionation column 1178 as reflux. The separation of theliquid from the overhead stream via the reflux separator 1182 results inthe production of a vapor stream. The vapor stream may be a fuel streamincluding primarily nitrogen and other low boiling point gases. From thereflux separator 1182, the vapor stream is flowed through the first heatexchanger 1120. The vapor stream is then progressively compressed andchilled within a first compressor 1183, a first chiller 1184, a secondcompressor 1185, and a second chiller 1186. The compressed, chilledstream is then combined with a natural gas stream within the pipe joint1114, and the combined stream is flowed out of the hydrocarbonprocessing system 1100 as fuel 1118.

The bottoms stream that is produced within the cryogenic fractionationcolumn 1178 includes primarily LNG with traces of nitrogen. The LNG isflowed through the reflux condenser 1181 and is used to cool theoverhead stream from the cryogenic fractionation column 1178. As the LNGstream exchanges heat with the overhead stream, it is partiallyvaporized, producing a multiphase natural gas stream.

The multiphase natural gas stream is flowed into a third flash drum1187, which separates the multiphase natural gas stream into a naturalgas stream and an LNG stream. The natural gas stream is combined withinanother natural gas stream within a pipe joint 1188, compressed within acompressor 1189, chilled within a chiller 1190, and combined with theinitial natural gas stream within the pipe joint 1124.

From the third flash drum 1187, the LNG stream is flowed through anexpansion device 1191, such as an expansion valve or hydraulic expander,that controls the flow of the natural gas stream into a fourth flashdrum 1192. The expansion device 1191 reduces the temperature andpressure of the natural gas stream, resulting in the flash evaporationof the natural gas stream into both a natural gas stream and an LNGstream. The natural gas stream is then separated from the LNG steam viathe fourth flash drum 1192.

The natural gas stream is flowed from the fourth flash drum 1192 into apipe joint 1193, in which the natural gas stream is combined withanother natural gas stream. The combined natural gas stream iscompressed within a compressor 1194 and then flowed into the pipe joint1188 to be combined with the natural gas stream from the third flashdrum 1187.

From the fourth flash drum 1192, the LNG stream is flowed into an LNGtank 1195. The LNG tank 1195 may store the LNG stream for any period oftime. Boil-off gas generated within the LNG tank 1195 is flowed to thepipe joint 1193 and combined within the natural gas stream from thefourth flash drum 1192. At any point in time, the final LNG stream 1108may be transported to a LNG tanker 1196 using a pump 1197, for transportto markets. Additional boil-off gas 1198 generated while loading thefinal LNG stream 1108 into the LNG tanker 1196 may be recovered in thehydrocarbon processing system 1100.

Method for LNG Production

FIG. 12 is a process flow diagram of a method 1200 for the formation ofLNG from a natural gas stream using a mixed fluorocarbon refrigerant.The method 1200 may be implemented within any suitable type ofhydrocarbon processing system. For example, the method 1200 may beimplemented by any of the hydrocarbon processing systems 500 or 800−1100discussed with respect to FIGS. 5-11.

The method 1200 begins at block 1202, at which a natural gas is cooledto produce LNG in a fluorocarbon refrigeration system using a mixedfluorocarbon refrigerant. The mixed fluorocarbon refrigerant may includeany suitable mixture of fluorocarbon components, or any suitable mixtureof fluorocarbon components and other non-flammable components, such asinert compounds. For example, the mixed fluorocarbon refrigerant may bea mixture of any number of different HFCs, HFOs, and/or inert compounds.

Cooling the natural gas in the fluorocarbon refrigeration system mayinclude compressing the mixed fluorocarbon refrigerant to provide acompressed mixed fluorocarbon refrigerant and cooling the compressedmixed fluorocarbon refrigerant by indirect heat exchange with a coolingfluid to provide a cooled mixed fluorocarbon refrigerant. The cooledmixed fluorocarbon refrigerant may then be passed to a heat exchangearea, and the natural gas may be cooled by indirect heat exchange withthe cooled mixed fluorocarbon refrigerant in the heat exchange area.

The fluorocarbon refrigeration system may be any suitable type ofrefrigeration system that is capable of cooling a natural gas streamusing a mixed fluorocarbon refrigerant. For example, the fluorocarbonrefrigeration system may be an SMR cycle, DMR cycle, TMR cycle, orpre-cooled MR cycle. If the fluorocarbon refrigeration system is a DMRcycle, for example, the fluorocarbon refrigeration system may include afirst MR cycle that uses a warm mixed fluorocarbon refrigerant and asecond MR cycle that uses a cold mixed fluorocarbon refrigerant. Thefirst mixed refrigerant cycle and the second mixed refrigerant cycle maybe connected in series.

At block 1204, nitrogen is removed from the LNG in an NRU. In someembodiments, the nitrogen stream separated from the natural gas via theNRU is used to further cool at least a portion of the natural gas.

In various embodiments, the natural gas is further cooled to produce theLNG in an autorefrigeration system. The autorefrigeration system mayinclude a number of expansion devices and flash drums for cooling thenatural gas. In addition, in some embodiments, the natural gas isfurther cooled to produce the LNG in a nitrogen refrigeration systemusing a nitrogen refrigerant. The nitrogen refrigeration system may belocated upstream of the autorefrigeration system, for example.

It is to be understood that the process flow diagram of FIG. 12 is notintended to indicate that the blocks of the method 1200 are to beexecuted in any particular order, or that all of the blocks are to beincluded in every case. Further, any number of additional blocks may beincluded within the method 1200, depending on the details of thespecific implementation.

Embodiments

Embodiments of the techniques may include any combinations of themethods and systems shown in the following numbered paragraphs. This isnot to be considered a complete listing of all possible embodiments, asany number of variations can be envisioned from the description herein.

1. A hydrocarbon processing system for liquefied natural gas (LNG)production, including:

-   -   a fluorocarbon refrigeration system configured to cool a natural        gas to produce LNG using a mixed fluorocarbon refrigerant; and    -   a nitrogen rejection unit (NRU) configured to remove nitrogen        from the LNG.

2. The hydrocarbon processing system of paragraph 1, including anitrogen refrigeration system configured to further cool the natural gasto produce the LNG using a nitrogen refrigerant.

3. The hydrocarbon processing system of any of paragraphs 1 or 2,including an autorefrigeration system configured to further cool thenatural gas to produce the LNG.

4. The hydrocarbon processing system of paragraph 3, wherein theautorefrigeration system includes a number of flash drums and a numberof expansion devices.

5. The hydrocarbon processing system of any of paragraphs 1-3, whereinat least a portion of the natural gas is cooled using a nitrogen streamseparated from the natural gas via the NRU.

6. The hydrocarbon processing system of any of paragraphs 1-3 or 5,wherein the fluorocarbon refrigeration system includes a single mixedrefrigerant cycle.

7. The hydrocarbon processing system of any of paragraphs 1-3, 5, or 6,wherein the fluorocarbon refrigeration system includes a pre-cooledmixed refrigerant cycle.

8. The hydrocarbon processing system of any of paragraphs 1-3 or 5-7,wherein the fluorocarbon refrigeration system includes a dual mixedrefrigerant cycle.

9. The hydrocarbon processing system of paragraph 8, wherein the dualmixed refrigerant cycle includes:

-   -   a first mixed refrigerant cycle that uses a warm mixed        fluorocarbon refrigerant; and    -   a second mixed refrigerant cycle that uses a cold mixed        fluorocarbon refrigerant, wherein the first mixed refrigerant        cycle and the second mixed refrigerant cycle are connected in        series.

10. The hydrocarbon processing system of any of paragraphs 1-3 or 5-8,wherein the fluorocarbon refrigeration system includes a triple mixedrefrigerant cycle.

11. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or10, wherein the fluorocarbon refrigeration system includes a heatexchanger configured to allow for cooling of the natural gas via anindirect exchange of heat between the natural gas and the mixedfluorocarbon refrigerant.

12. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, 10,or 11, wherein the fluorocarbon refrigeration system includes:

a compressor configured to compress the mixed fluorocarbon refrigerantto provide a compressed mixed fluorocarbon refrigerant;

a chiller configured to cool the compressed mixed fluorocarbonrefrigerant to provide a cooled mixed fluorocarbon refrigerant; and

a heat exchanger configured to cool the natural gas via indirect heatexchange with the cooled mixed fluorocarbon refrigerant.

13. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or10-12, wherein the hydrocarbon processing system is configured to chillthe natural gas for hydrocarbon dew point control.

14. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or10-13, wherein the hydrocarbon processing system is configured to chillthe natural gas for natural gas liquid extraction.

15. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or10-14, wherein the hydrocarbon processing system is configured toseparate methane and lighter gases from carbon dioxide and heaviergases.

16. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or10-15, wherein the hydrocarbon processing system is configured toprepare hydrocarbons for liquefied petroleum gas production storage.

17. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or10-16, wherein the hydrocarbon processing system is configured tocondense a reflux stream.

18. A method for liquefied natural gas (LNG) production, including:

cooling a natural gas to produce LNG in a fluorocarbon refrigerationsystem using a mixed fluorocarbon refrigerant; and

-   -   removing nitrogen from the LNG in a nitrogen rejection unit        (NRU).

19. The method of any of paragraphs 18, including further cooling thenatural gas to produce the LNG in a nitrogen refrigeration system usinga nitrogen refrigerant.

20. The method of any of paragraphs 18 or 19, including further coolingthe natural gas to produce the LNG in an autorefrigeration system.

21. The method of paragraph 20, including cooling at least a portion ofthe natural gas using a nitrogen stream separated from the natural gasvia the NRU.

22. The method of any of paragraphs 18-20, wherein cooling the naturalgas in the fluorocarbon refrigeration system includes:

-   -   compressing the mixed fluorocarbon refrigerant to provide a        compressed mixed fluorocarbon refrigerant;    -   cooling the compressed mixed fluorocarbon refrigerant by        indirect heat exchange with a cooling fluid to provide a cooled        mixed fluorocarbon refrigerant;    -   passing the cooled mixed fluorocarbon refrigerant to a heat        exchange area; and heat exchanging the natural gas with the        cooled mixed fluorocarbon refrigerant in the heat exchange area.

23. A hydrocarbon processing system for formation of a liquefied naturalgas (LNG), including:

-   -   a mixed refrigerant cycle configured to cool a natural gas using        a mixed fluorocarbon refrigerant, wherein the mixed refrigerant        cycle includes a heat exchanger configured to allow for cooling        of the natural gas via an indirect exchange of heat between the        natural gas and the mixed fluorocarbon refrigerant;    -   a nitrogen rejection unit (NRU) configured to remove nitrogen        from the natural gas; and    -   a methane autorefrigeration system configured to cool the        natural gas to produce the LNG.

24. The hydrocarbon processing system of paragraph 23, wherein the mixedfluorocarbon refrigerant includes a mixture of two or morehydrofluorocarbon refrigerants.

25. The hydrocarbon processing system of any of paragraphs 2 or 24,wherein a nitrogen stream separated from the natural gas via the NRU isused to cool at least a portion of the natural gas.

26. The hydrocarbon processing system of any of paragraphs 23-25,wherein the methane autorefrigeration system includes a number ofexpansion devices and a number of flash drums.

While the present techniques may be susceptible to various modificationsand alternative forms, the embodiments discussed herein have been shownonly by way of example. However, it should again be understood that thetechniques is not intended to be limited to the particular embodimentsdisclosed herein. Indeed, the present techniques include allalternatives, modifications, and equivalents falling within the truespirit and scope of the appended claims.

1. A hydrocarbon processing system for liquefied natural gas (LNG)production, comprising: a fluorocarbon refrigeration system configuredto cool a natural gas to produce LNG using a mixed fluorocarbonrefrigerant; a nitrogen rejection unit (NRU) configured to removenitrogen from the LNG; and an autorefrigeration system configured tofurther cool the natural gas to produce the LNG.
 2. The hydrocarbonprocessing system of claim 1, comprising a nitrogen refrigeration systemconfigured to further cool the natural gas to produce the LNG using anitrogen refrigerant.
 3. (canceled)
 4. The hydrocarbon processing systemof claim 1, wherein the autorefrigeration system comprises a pluralityof flash drums and a plurality of expansion devices.
 5. The hydrocarbonprocessing system of claim 1, wherein at least a portion of the naturalgas is cooled using a nitrogen stream separated from the natural gas viathe NRU.
 6. The hydrocarbon processing system of claim 1, wherein thefluorocarbon refrigeration system comprises a single mixed refrigerantcycle.
 7. The hydrocarbon processing system of claim 1, wherein thefluorocarbon refrigeration system comprises a pre-cooled mixedrefrigerant cycle.
 8. The hydrocarbon processing system of claim 1,wherein the fluorocarbon refrigeration system comprises a dual mixedrefrigerant cycle.
 9. The hydrocarbon processing system of claim 8,wherein the dual mixed refrigerant cycle comprises: a first mixedrefrigerant cycle that uses a warm mixed fluorocarbon refrigerant; and asecond mixed refrigerant cycle that uses a cold mixed fluorocarbonrefrigerant, wherein the first mixed refrigerant cycle and the secondmixed refrigerant cycle are connected in series.
 10. The hydrocarbonprocessing system of claim 1, wherein the fluorocarbon refrigerationsystem comprises a triple mixed refrigerant cycle.
 11. The hydrocarbonprocessing system of claim 1, wherein the fluorocarbon refrigerationsystem comprises a heat exchanger configured to allow for cooling of thenatural gas via an indirect exchange of heat between the natural gas andthe mixed fluorocarbon refrigerant.
 12. The hydrocarbon processingsystem of claim 1, wherein the fluorocarbon refrigeration systemcomprises: a compressor configured to compress the mixed fluorocarbonrefrigerant to provide a compressed mixed fluorocarbon refrigerant; achiller configured to cool the compressed mixed fluorocarbon refrigerantto provide a cooled mixed fluorocarbon refrigerant; and a heat exchangerconfigured to cool the natural gas via indirect heat exchange with thecooled mixed fluorocarbon refrigerant.
 13. The hydrocarbon processingsystem of claim 1, wherein the hydrocarbon processing system isconfigured to chill the natural gas for hydrocarbon dew point control.14. The hydrocarbon processing system of claim 1, wherein thehydrocarbon processing system is configured to chill the natural gas fornatural gas liquid extraction.
 15. The hydrocarbon processing system ofclaim 1, wherein the hydrocarbon processing system is configured toseparate methane and lighter gases from carbon dioxide and heaviergases.
 16. The hydrocarbon processing system of claim 1, wherein thehydrocarbon processing system is configured to prepare hydrocarbons forliquefied petroleum gas production storage.
 17. The hydrocarbonprocessing system of claim 1, wherein the hydrocarbon processing systemis configured to condense a reflux stream.
 18. A method for liquefiednatural gas (LNG) production, comprising: cooling a natural gas toproduce LNG in a fluorocarbon refrigeration system using a mixedfluorocarbon refrigerant; [[and]] removing nitrogen from the LNG in anitrogen rejection unit (NRU); and further cooling the natural gas toproduce the LNG in an autorefrigeration system.
 19. The method of claim18, comprising further cooling the natural gas to produce the LNG in anitrogen refrigeration system using a nitrogen refrigerant. 20.(canceled)
 21. The method of claim 18, comprising cooling at least aportion of the natural gas using a nitrogen stream separated from thenatural gas via the NRU.
 22. The method of claim 18, wherein cooling thenatural gas in the fluorocarbon refrigeration system comprises:compressing the mixed fluorocarbon refrigerant to provide a compressedmixed fluorocarbon refrigerant; cooling the compressed mixedfluorocarbon refrigerant by indirect heat exchange with a cooling fluidto provide a cooled mixed fluorocarbon refrigerant; passing the cooledmixed fluorocarbon refrigerant to a heat exchange area; and heatexchanging the natural gas with the cooled mixed fluorocarbonrefrigerant in the heat exchange area.
 23. A hydrocarbon processingsystem for formation of a liquefied natural gas (LNG), comprising: amixed refrigerant cycle configured to cool a natural gas using a mixedfluorocarbon refrigerant, wherein the mixed refrigerant cycle comprisesa heat exchanger configured to allow for cooling of the natural gas viaan indirect exchange of heat between the natural gas and the mixedfluorocarbon refrigerant; a nitrogen rejection unit (NRU) configured toremove nitrogen from the natural gas; and a methane autorefrigerationsystem configured to cool the natural gas to produce the LNG.
 24. Thehydrocarbon processing system of claim 23, wherein the mixedfluorocarbon refrigerant comprises a mixture of two or morehydrofluorocarbon refrigerants.
 25. The hydrocarbon processing system ofclaim 23, wherein a nitrogen stream separated from the natural gas viathe NRU is used to cool at least a portion of the natural gas.
 26. Thehydrocarbon processing system of claim 23, wherein the methaneautorefrigeration system comprises a plurality of expansion devices anda plurality of flash drums.